1. Field of the Invention
This invention relates to an exhaust gas recirculation system of an engine which controls intake and exhaust valves for opening and closing by electromagnetic force.
2. Description of the Prior Art
A conventional electronic control engine for controlling intake and exhaust valves in accordance with the operational conditions of an engine is disclosed, for example, in Japanese Patent Laid-Open No. 162312/1984. This electronic control engine controls the intake and exhaust valves of the engine for opening and closing by electromagnetic force, and includes means for inputting the operational conditions of the engine and the atmospheric conditions, sampling data per predetermined crank angle and determining opening/closing timings of the intake and exhaust valves, their lift characteristics, the ON/OFF time ratio and the injection quantity of an injector, means for outputting driving signals per predetermined crank angle to solenoids of the intake and exhaust valves and means for outputting the driving signals to the injection when the exhaust valves are open.
Generally, an exhaust gas recirculation system of an engine limits the occurence of NOx by mixing part of the exhaust gas with the intake air and the exhaust gas recirculation ratio is expressed by a mass ratio of the exhaust gas quantity to the total gas quantity sucked in exhaust gas recirculation. In other words, the exhaust gas recirculation ratio r.sub.EGR can be expressed as follows with m.sub.EGR and m.sub.IN being the recirculated exhaust gas quantity and the intake air-fuel quantity, respectively: EQU r.sub.EGR =m.sub.EGR /(m.sub.EGR +m.sub.IN)
In the exhaust gas recirculation system of an engine, however, it is difficult to detect the exhaust gas recirculation flow rate passing into a combustion chamber when exhaust gas recirculation is effected by the valve motion of the valves. Since the exhaust gas recirculation flow rate cannot be known, the exhaust gas recirculation flow rate to be introduced into the combustion chamber cannot be regulated. Therefore, when exhaust gas recirculation is executed by the valve motion of the exhaust valves, there remains the problem how the exaust gas recirculation flow rate can be detected and how the valve lift quantity and valve opening time of the exhaust valve can thereby be regulated in order to determine the optimum exhaust gas recirculation flow rate for the load and number of revolution of the engine and to bring the exhaust gas recirculation flow rate close to the optimum exhaust gas recirculation flow rate in response to the exhaust gas recirculation flow rate thus detected.
An example of the prior art exhaust gas recirculation controllers is described in Japanese Patent Laid-Open No. 51747/1987, for example. This exhaust gas recirculation controller includes a reflux pipe for refluxing the exhaust gas of an internal combustion engine to an intake pipe, opening/closing means for opening and closing the reflux pipe, control means for controlling the opening/closing means for opening and closing, intake air detection means for detecting the intake air quantity to the intake pipe, memory means for storing separately the detected values from the detection means when the opening/closing means is opened and closed by the control means, judgement means for judging whether or not the difference between the detected values is within a predetermined range, upon receiving the detected values from the memory means, and alarm means for raising an alarm when the difference is judged to be within the predetermined range by the judgement means. This exhaust gas reflux controller or the gas recirculation apparatus includes the reflux pipe for refluxing the exhaust gas to the intake pipe and the opening/closing means for opening and closing the reflux pipe, and the exhaust gas is subjected to exhaust gas recirculation through the intake pipe and the intake valve. Therefore, contamination of the intake system by the exhaust gas is remarkable and there remain the problems that adjustment of the exhaust gas recirculation flow rate cannot be made and a large quantity of exhaust gas cannot be recirculated.
The exhaust gas recirculation apparatus of an internal combustion engine is disclosed in Japanes Patent Publication No. 34526/1976, for example. In a four-cycle internal combustion engine of the type wherein the exhaust valve of the same cylinder is opened for a short period immediately before or after the end of the intake stroke and part of the exhaust gas in the exhaust pipe is sucked into the cylinder during the intake stroke, the exhaust gas recirculation apparatus of this prior art reference connects the exhaust pipe of a certain cylinder whose intake valve is in the closing period to the exhaust pipe of a cylinder whose exhaust valve is in the opening period and disposes a valve which cuts off the communication between both exhaust pipes with an exhaust aggregate pipe when the exhaust valves are open for the short period described above, at the junction of each exhaust pipe with the exhaust aggregate pipe.
This exhaust gas recirculation apparatus disposes further a valve which cuts off the communication between each exhaust pipe and the exhaust aggregate pipe when each exhaust pipe is open for the short period described above, at the junction between each exhaust pipe and the exhaust aggregate pipe. The opening and closing operation of each exhaust valve for the purpose of exhaust gas recirculation, that is, the valve motion mechanism, is effected by a cam rope disposed at a cam. Accordingly, once the shape of the cam is determined and the cam is produced, the valve lift quantity and valve timing of the exhaust valve are determined so that the exhaust gas recirculation flow rate cannot be adjusted. Accordingly, it is not possible to adjust the exhaust gas recirculation flow rate in accordance with the operational conditions of the engine such as the change of the atmospheric pressure, the change of the number of revolution of the engine, the temperature change, the change of the engine load, and so forth.